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Formulation of Bio-Based with Industrial Application Adriana Marisa Bentes Correia Instituto Superior Tecnico´ Universidade de Lisboa [email protected]

Abstract—Bio-based polyols are synthesized from wastes such vegetable oils is usually carried out with performic or peracetic as used cooking oils, and from compounds present on orange, acid formed in-situ by reaction of hydrogen peroxide and the tomato, and pine (i.e. (+)-limonene, lycopene, and α-pinene, fatty acid, in presence or absence of catalysts. [2], [3], [4], respectively). In this work, we synthesized the polyols by using a one-pot reaction. To achieve this, a performic acid epoxidation (in [5], [6], [7] situ) opens the epoxides with water at different reaction times in The used cooking oils (UCO) are the result of the frying pro- a temperature of 65◦C at atmospheric pressure. The obtained cess of cooking oils and are constituted mainly by vegetable polyols were characterized using Fourier Transform Infrared oils, namely sunflower oil. This type of waste is obtained Spectroscopy (FTIR), Proton Nuclear Magnetic Resonance Spec- 1 from domestic and restoration sectors and has to be treated. In troscopy ( H NMR) and the refractive index (nD).The number of hydroxyl groups was determined a value in a range of 129 up Portugal, the UCO have, as the main destination, the to 215 mg KOH / g. The resultant adhesives were network causing problems in channeling and in performance synthesized adding methylene diphenyl diisocyanate (MDI) and and functioning of wastewater treatment plants. This waste is diisocyanate (TDI) to the polyols. Preliminary also disposed of illegally in landfills causing environmental tests with these indicated that it can be probably impact with the pollution of the surroundings. Currently, there used to produce more ecological glue in the footwear . The economic evaluation shows that the investment has the are companies that are responsible for the treatment and potential to address the environmental and economic challenges distribution of the UCO and also the transportation until the of waste cocking oil contributing to improve the sustainability of companies that recycle this waste. The main use of UCO in glue industry. the industry is to produce biodiesel, soaps and animal feed. Keywords—Cooking oil, Natural waste, Polyols, Polyurethane The market is saturated and is necessary to investigate other adhesives, Footwear industry methods to reuse the UCO. The main difference between UCO and new cooking oil (NCO) is the composition of free fatty acids that is greater in UCO than NCO. As one of the reactive I.INTRODUCTION sites of triglycerides is the carbon-carbon double bonds (C=C), Environmental concerns and increasing price of crude oil other components that have C=C are potential raw material. have led to increased interest in the development of material The (+)-limonene and lycopene are extracted from orange oil based on bio-based and renewable resources. Vegetable oils are and tomato, respectively, that is also a waste that is produced one of the most promising sources due to their properties. The in the large amount in Portugal due to agricultural activities. polyurethanes are with a versatile range of properties The α-pinene is also a compound with C=C that is present in and applications. The synthesis consists on the polyaddition of pines, one of the major constituent of the Portuguese forest, polyisocyanates (usually a diisocyanate) to polyols. In indus- that urgently need management solutions to control the fires. try, limited types of polyisocyanates are available. However, These compounds have the reactive sites that are required to there are a wide variety of petroleum-based polyols resources hydroxylate the compounds. or bio-based resources. The most common source for bio- In this study, a series of polyols were prepared by epoxi- based polyol is vegetable oils. [1], [2] dation/ring opening from different types of cooking oils, (+)- The major constituents of vegetable oils are triglyceride limonene, lycopene, and α − pineno. The main goal of this molecules, which are fatty acids triesters of glycerol. The work is to produce bio-based polyols starting from waste fatty acids commonly present in vegetable oils are palmitic cooking oils (+)-limonene, lycopene, and α-pineno in order to acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic obtain a more ecological formulation. The conversion acid (C18:2) and linolenic acid (C18:3). The reactive sites of triglyceride double bonds to epoxide rings followed by their of triglycerides are bonds, carbon-carbon double bonds conversion to the hydroxyl groups occurs in a single step. (C=C) and hydroxyl groups (OH). The OH groups are among Epoxidation is carried out by performic acid generated in situ the most important groups to synthesize the polyols. [1], [2] with formic acid/hydrogen peroxide and ring opening by water Although some vegetable oils have OH groups due to the in acidic media. presence of the fatty acid ricinoleic (C18:1 OH), the majority This work was developed in partnership with the company has to be functionalized. One of the most popular and effective CIPADE. This company produces adhesives for several sec- routes to achieve it is through epoxidation. The epoxidation of tors, including the Footwear Industry. 2

II.RELATED WORK the required time, the reaction mixture was washed firstly The epoxidation/oxirane ring opening methods have been with a sodium bisulfite 10% (w/v) solution and after with widely investigated for the preparation of bio-based polyols sodium carbonate, 10% (w/v) solution until neutralization for polyurethane production. In these methods occurs the had occurred. Lastly, diethyl ether was added to separate the epoxidation of unsaturated bonds, followed by ring-opening organic phase. The organic phase was dried overnight with reactions of the oxirane rings. The nucleophilic reagents can magnesium sulfate anhydrous. The was removed under be amines, carboxylic acids, halogenated acids or alcohols. [7] vacuum using a rotatory evaporator. In some developed researches water, mono-hydroxy alco- hols and poly-hydroxy alcohols were used as nucleophilic reagents for ring-opening of epoxides. The ring-opening re- action is frequently catalyzed with inorganic acids, such as phosphoric acid, sulphuric acid, fluoroboric acid and Lewis acids. [8], [9], [10] In [4] was prepared a series of polyols from ESO using methanol, glycol, and 1,2-propanediol as ring- opening nucleophiles. The prepared polyols had a range of OH number varying from 148 to 240 mg KOH/g. Using a similar pathway, in [11], [12] were prepared polyols through ring-opening epoxidized vegetable oils using bio-based 1,2- propanediol and 1,3-propanediol. In [13] methanol was used to ring-open epoxidized Jatropha oil to prepare polyols with hydroxyl content from 171 to 179 mg KOH/g. In this study, the authors also reported that the application of more concentrated hydrogen peroxide in the solvent-free epoxidation process accelerated the epoxidation reaction, resulting in minimum side reactions and the maximum value of oxirane rings content. In [14] bio-based polyols were prepared by ring-opening of epoxidized rapeseed oil using . Using greener nucleophiles, in [2] was used water as a Fig. 1. Experimental apparatus were is possible see the reactor (a) and the heating system (b). reagent for ring-opening of epoxidized vegetable oils. It was also reported that epoxidation and the hydroxylation of veg- An analog procedure was done for linseed oil, (+)-limonene, etable oils can be performed in one single step using performic lycopene, and α − pinene with an adjustment of the reagents acid prepared in situ with the reaction between hydrogen quantity (Table I). peroxide and formic acid. TABLE I III.MATERIALS AND METHODS QUANTITYOFREAGENTS. A. Synthesis of bio-based Polyols Formic Hydrogen Mass Chemicals Acid Peroxide (g) The used cooking oils were obtained by domestic utilities, (mL) (mL) the linseed oil was purchased from the brand Emile Noel, linseed oil 35 30,8 36,2 the cooking oil was purchased from the brand fula, (+)- (+)-limonene 35 29,6 34,8 limonene was extracted by steam distillation from orange oil lycopene 35 49,0 58,0 purchased from Sumol, lycopene was extracted by Soxhlet α − pinene 35 15,1 17,7 extraction from tomatoes and α-pinene was purchased from Fluka Chemie AG. Formic acid 98% and sodium bisulfite were purchased from Merck. Hydrogen peroxide solution 30%, diethyl ether and magnesium sulfate anhydrous were B. Determination of Hydroxyl Value of Polyols purchased from Panreac. Sodium carbonate was purchased Chemicals from Univar. All chemicals are analytical grade and were used Potassium hydroxide (KOH) 0,1 N and 0,5 N were pur- without further purification. chased from Fluka. 4-N, N-dimetilaminopiridine, phenolph- Procedure thalein, and thymolphthalein were purchased from Merk. Cooking oils (35g, 0,19 mol of double bonds) were mixed Acetic anhydride and tetrahydrofuran (THF) were purchased with 21,5 mL (1,11 mol) of formic acid. A solution of H2O2, from Sigma.All chemicals are analytical grade and were used 30% (25,3 mL; 0,28 mol) was slowly added dropwise to without further purification. the mixture at room temperature over 30 min, under strong Procedure mechanical stirring. When the H2O2 addition was completed, The hydroxyl (OH) content of the polyols was determined the mixture was heated at 65◦C, Figure 1. The procedure by titration methods. To determine the hydroxyl value is also was repeated with reaction times between 1-5 hours. After necessary to obtain the acid value (AV). To obtain the AV, 40 3 mL of THF and 3 drops of pH indicator phenolphthalein were F. Synthesis of Polyurethane Adesives added into 1 g of the polyols. The mixture was titrated with Chemicals a KOH 0,1 N solution. For each polyol, the procedure was Methylene diphenyl diisocyanate (MDI) and toluene diiso- done in triplicate. The AV has determined accordingly with cyanate (TDI) were supplied by CIPADE. Equation 1. Procedure To obtain the polyurethane adhesives were added a percent- VKOH × N × MWKOH AV = (1) age of di-isocyanate at 4 g of the polyols. Accordingly to w sample CIPADE the amount of di-isocyanate added is 5% of total −1 where MWKOH = 56, 1g.mol , VKOH is the titrant weight of the polyols sample. This value is used for the volume, N is the titrant concentration and wsample is the petroleum-based polyols that this company produce. To know sample weight used the percentage of di-isocyanate to add, the OH values of the To determine the OH value it was necessary to prepare 3 CIPADE polyols were determined and compared with the OH solutions: values of the bio-based polyols. In the Table II the mass percentages over the total amount of polyol of di-isocyanate 1) Catalyst solution: 1% 4-N,N-dimetilaminopiridine in to add at bio-based polyols obtained from new cooking oil THF; (NCO), used cooking oil (UCO), very used cooking oil 2) Acetyl solution: 12,5% of acetic anhydride in THF; (VUCO) and new linseed oil (NLO) for reaction times of 1h, 3) pH indicator solution: 1% thymolphthalein in THF. 3h and 5h are showed. At 1g of polyols was added 40 mL of THF, 10 mL of catalyst solution and 10 mL of acetyl solution. The mixture TABLE II was stirred for 10 minutes. Then 2 mL of distilled water was MASS PERCENTAGE OF DI-ISOCYNATE TO ADD AT BIO-BASED POLYOLS. added and the mixture was stirred for more 30 minutes. After Polyols MDI (%) TDI (%) the stirred time, 3 drops of thymolphthalein solution were UCO 1h 26 49 added and the mixture was titrated with KOH 0,5 N. For each UCO 3h 15 29 polyol, the procedure was done in triplicate. The OH value UCO 5h 23 43 was calculated accordingly with Equation 2. VUCO 1h 19 35 VUCO 3h 17 32 MW × N × (V − V ) OH = KOH S KOH + AV (2) VUCO 5h 11 21 wsample NCO 1h 18 34 NCO 3h 5 9 where MW = 56, 1g.mol−1, V is the titrant KOH KOH NCO 5h 19 35 volume,V is the volume of standard sample (all the reagents S NLO 1h 39 72 were added except the polyols), N is the titrant concentration, NLO 3h 15 27 w is the sample weight used and AV is the acid value sample NLO 5h 13 24 previously determined.

C. Refractive Index G. Glue Tests Instrumentation The glue tests were done using a specific that was The refractive index of the polyols was measured in an Abbe supplied from CIPADE. This paper is the same that they use refractometer from CARL ZEISS. to test their own adhesives. The polyurethane adhesives were applied to the paper using an applicator as shown in Figure 2. D. Fourier Transfrom Infrared Spectroscopy The paper was cut into strips (Figure 3). After 30 minutes one of the strips was evaluated by separating the ends of the Instrumentation paper. The same procedure was done every one hour until the The Fourier Transform Infrared Spectroscopy (FTIR) spec- paper rips when being taken off, a positive result. trum was determined using sodium chloride disks (NaCl) and the equipment FTIR-8400S from SHIMADZU. The spectra IV. RESULTS AND DISCUSSION were obtained with 32 scans and a resolution of 4,0. A. Synthesis and Characterization of the Polyols In this work, the bio-based polyols were synthesized from E. Proton Nuclear Magnetic Resonance Spectroscopy different types of raw materials. Regarding the , the polyols synthesized from NLO and VUCO showed a higher Instrumentation viscosity, than others. Regarding the smell, the cooking oil The Proton Nuclear Magnetic Resonance Spectroscopy (1H polyols had no odor of used oil, as well as the lycopene RMN) spectra were determined using the equipment Bruker and α − pinene polyols. On the other hand, the polyols 300 UltrashieldT M type Magnet System 300 MHz/54 mm. synthesized from (+)-limonene preserved the characteristic 4

Fig. 4. Polyols obtained from NCO, UCO and VCO, from left to right

Fig. 2. Application of the polyurethane adhesives at the test paper. requirements, as they are promising for the adhesives formu- lation and application to the shoes. While the other residues used for polyol synthesis are also promising, it is necessary to research more methods for its synthesis that includes the addition of color and odor-eliminating components. The polyols were synthesized from new cooking oil (NCO), used cooking oil (UCO), very used cooking oil (VUCO) and new linseed oil (NLO) with yields between 23% and 91%. The differences among yelds values are caused by experimental errors. Table III shows the yields according to its reaction time. Comparing the yields with the reaction time, it is possible to infer that the yield generally reaches its maximum value with 3 hours of reaction.

Fig. 3. Rips of paper glued by bio-based polyurethane adhesives. TABLE III THEYIELDOFTHESYNTHESISPROCESSOFTHEPOLYOLSTHROUGH DIFFERENT TYPES OF RAW MATERIALS ALONG WITH DIFFERENT REACTIONTIMES.*NSNOTSYNTHESIZED,*RQRESIDUALQUANTITIES odor of its compound, indicating that (+)-limonene did not react completely. Yield (%) 1h 2h 3h 4h 5h In terms of coloring, the polyols from pre- NCO 75 61 60 62 64 sented a colorless appearance, except for the polyols obtained UCO 63 56 82 73 43 from VUCO and NLO, which in this had a yellow VUCO 23 37 55 49 48 coloration. The yellow coloration was expected, once the oil OLN 80 49 91 57 46 was exposed to a long frying time at high temperatures causing (+)-limonene ns ns rq ns 27 a change in its color, consequently, in the obtained polyol. So, α − pinene ns ns 38 ns 15 the (+)-limonene polyols showed a brown coloration while the Lycopene ns ns rq ns rq lycopene and α−pinene polyols showed a yellow coloration. The Figure 4 shows some polyols samples along with its Regarding the (+)-limonene and α − pinene polyols, the respective coloration. obtained yields are between 15% and 38%. The quantity of polyol obtained from lycopene was residual, making it B. Synthesis and Characterization of the polyurethane Adhe- impossible to calculate its yield. Due to the low yields obtained sives from these compounds, we decided to proceded the study only The color can be an important factor to choose an adhesive considering the polyols obtained from oils. among other, especially in the footwear context. If the adhesive The results obtained from the titration procedures indicate is used to attach the tops of the shoes to the sole, its color may that the bio-based polyols have an amount of hydroxyl groups not affect the choice of the polyol. Although if the adhesive (OH) of 129-293 mg KOH/g and an acid value (AV) between is used to paste exposed areas of the shoes, it is necessary 13-106 mg KOH/g (Table IV). The determined OH values to ensure that the design of the shoes are not affected by the are similar to those obtained in the literature. [4], [11], [12], color of the polyols. [13], [2]. It is important to note that the different amounts of The smell is another important factor to take into consider- OH and AV between the bio-based polyols and the CIPADE ation because it can drastically affect the consumer demand. polyols (which are obtained from petroleum sources) have In general, the cooking oil polyols meets the smell and color lower OH and AV values. The differents AV and OH values 5 are due to the higher molecular weight of CIPDADE polyols (4000-6000 g/mol) compared to bio-based polyols (1650-2000 g/mol). CIPADE produces specific polyols for each type of diisocyanate. For example, the polyol CIPADE 1 is specific for MDI addition while and the Polyol CIPADE 2 is specific for TDI addition. We can conclude that the obtained bio-based polyols have OH groups which can be used in the preparation of polyurethane adhesives.

TABLE IV ACIDVALUESANDHYDROXYLGROUPSPRESENTINSYNTHESIZED POLYOLS FROM VEGETABLE OILS. Polyols AV (mg KOH/g) OH (mg KOH/g) UCO 1h 72 170 UCO 3h 42 162 UCO 5h 63 138 VUCO 1h 51 129 Fig. 5. Evolution of the refractive index with the reaction time. VUCO 3h 46 140 VUCO 5h 30 185 polyols show similar results and are in agreement with the NCO 1h 49 215 literature. [4], [11], [12], [13], [2] NCO 3h 13 170 NCO 5h 52 223 NLO 1h 106 293 NLO 3h 40 218 NLO 5h 36 254 Polyol CIPADE 1 8 14 Polyol CIPADE 2 2 7

Figure 5 shows the evolution of refractive index of the bio-based polyols (y-axis) with the reaction time (x-axis) applied to each type of raw material.At reaction time zero, the refractive index values correspond to the cooking oils before any reaction. In this situation, the NLO and VUCO have the highest refractive index, while NCO is the oil with the lowest refractive index. In terms of used cooking oils, it is possible to verify that the frying time is directly related to the refractive index. The longer frying time, the higher refractive index, due to the higher viscosity. Analyzing the behavior of the refractive index of the bio- based polyols, it is possible to verify that the polyols obtained Fig. 6. FTIR spectra of the UCO and its respective polyols. from NLO and VUCO have a similar refractive index, due to higher polymerization. It has been previously shown that the In the 1H NMR spectra of UCO (Figure 7) it is visible polyols obtained from these oils had a yellow coloration and a hydrogen signal in the region 5,2-5,5 ppm assigned to the the highest viscosity. The refractive indexes of the NCO and C=C double bonds. In the polyols spectra, this signal does UCO polyols are also similar, suggesting that their composi- not appear. Instead, it appears a hydrogen signal at 2,6-2,9 tion is alike, having the higher refractive index for 3h reaction. ppm assigned to the groups for the polyol UCO 1h and Analyzing the UCO FTIR spectra and its respective polyols a hydrogen signal in the region 3,8-4,2 ppm assigned to the (Figure 6) it is possible to verify that the main difference OH groups for polyols UCO 1h and UCO 5h. In the spectra between the spectra of the oil and the bio-based polyols is of polyol UCO 5h, the hydrogen signal related to the epoxy the disappearance of the band at 3010 cm−1. Then, appears groups does not appear showing that all the epoxy rings were a large band at 3450 cm−1 assigned to the OH group. In opened. For the other polyols, a similar result was obtained. this way, it proves that the double bonds react completely, These results are also in agreement with the literature. [4], giving rise to the epoxide groups. Consequently, the ring opens [11], [12], [13], [2] leading to the desired functionalization with the OH group Once this work aims to synthesize bio-based polyols to formation. The spectra of the polyols show that regardless the replace petroleum-based polyols, we compared the FTIR reaction time the band corresponding to the C-H (present in spectra of the CIPADE petroleum-based polyols with FTIR the double bonds) disappears, indicating that all the unsatura- spectra of the bio-based polyols (Figure 8). Note that the tions were functionalized. The FTIR spectra of the remaining differences in the region of OH groups are expected because 6

Fig. 7. 1H NMR spectra of the UCO and its respective polyols. of the smaller amount of OH value in CIPADE polyols. This spectrum shows that the choice of the diisocyanate (according to the composition of the polyol) has a significant influence on the synthesis of the polyurethane. It is unclear which the diisocyanates are the most suitable for adding to the bio-based polyols once none of the polyols of CIPADE have similar spectra. Fig. 9. Reaction scheme for the PUR formulation.

Fig. 10. PUR adhesives by adding TDI (left) and MDI (right) to the polyol UCO 5h.

Fig. 8. FTIR spectra of the bio-based polyols and CIPADE polyols. between the spectra of the PUR samples, being unclear which The polyurethane adhesives (PUR) were synthesized with diisocyanate (MDI or TDI) must be used. These spectra are the addition of MDI and TDI at polyols. The reaction scheme in accordance with the literature. [2] for the synthesis of the polyols by epoxidation/ring opening The PUR were submitted to glue tests 30 minutes after the and addition of diisocyanate for the formulation of the PUR application. All the samples obtained negative results in this is shown in Figure 9. period. The same analyses were performed every 1 hour for 7 Analyzing the physical characteristics of PUR, we found consecutive hours, during this period the results remained neg- that they have a yellow coloration when the MDI diisocyanate ative. After 24 hours, some of the samples already presented is used while they are colorless when TDI is added. Figure 10 positive results, (i.e. the paper was torn when taking off). The shows a PUR sample formulated from polyol UCO 5h. glue tests results are summarized in Table V. Analyzing the FTIR spectra of PUR samples (Figure 11), The Figure 12 shows a positive and a negative test. it is possible to verify the appearance of a band in the region The PUR obtained through the polyols NLO 1h, NLO 3h, 2200-2240 cm−1 assigned to N=C group of the diisocyanates. NLO 5h, VUCO 1h, VUCO 3h, VUCO 5h and UCO 5h These spectra were traced after 1h of PUR synthesis. The band present positive results regardless of the type of diisocyanate at 3450 cm−1 is still visible showing that the OH groups have used. This can be related to the high viscosity of these polyols. not reacted completely. After 24h is expected that this signal The PUR obtained from the polyol UCO 1h has a positive test disappears due to the complete reaction of the diisocyanate when TDI is added. This result highlights the importance of with the OH groups of the polyols. The similarity is observed choosing a suitable diisocyanate. 7

cooking oils, the VUCO particularly, had a better behavior in the glue test than the NCO. This is in agreement with the objectives to be reached with this work. To finally conclude, these tests have many variables that can influence the results. To enhance the PUR performance it is necessary to optimize reagent quantities and reaction conditions.

V. INDUSTRIAL APPLICATION To investigate if the formulation of polyurethane adhesives (PUR) from used cooking oils (UCO) has industrial viability, a scale-up of the process and an economic evaluation was performed. The economic evaluation methods used estimated the process profitability at an early stage.

Fig. 11. FTIR spectra of the polyol UCO 5h and the respective polyurethane A. Scale-up adhesives (PUR). To synthesize bio-based polyols from UCO at industrial scale using a laboratory similar method, the equipment was TABLE V RESULTS OF GLUE TESTS. sized for an annual capacity of 10 kton. The amount of polyol produced is 1,263 ton/h, consuming 2,140 ton/h of UCO. Polyols MDI TDI In the process proposed, the reaction occurs in a stirring UCO 1h - + reactor, the neutralization and solvent extraction happens in UCO 3h - - tanks and the aqueous phase is eliminated in decanter vessels. UCO 5h + + The operations solid dry with magnesium sulfate anhydrous VUCO 1h + + and rotary evaporation were replaced with a flash distillation VUCO 3h + + column. The proposed flowsheet is shown in Figure 13. VUCO 5h + + NCO 1h - - NCO 3h - - NCO 5h - - LNO 1h + + LNO 3h + + LNO 5h + +

Fig. 13. Process Flowsheet to synthesize the polyol at industrial scale.

B. Economical Evaluation Fig. 12. Glue tests result. The economic evaluation of the process indicated in a first analysis that the process is profitable with a profitability index of 1,6. The capital is recovered in 6 years. The break-even at The polyols obtained from NCO have OH values higher 11% show that is possible reduces the plant capacity until 11% than the UCO and VUCO polyols. However, none of the PUR keeping the viability. samples synthesized with NCO polyols have positive tests. This result is unrelated with the polyols OH value because the positive tests are expected to occur on the polyols with VI.CONCLUSIONS the highest OH value. It can be related with the diisocyanate The bio-based polyols synthesized from epoxidation/ring ratio and type and also with the fact that some of the OH opening of cooking oils presented an average hydroxyl value groups are from the formic acid that not react completely. (OH) of 129-293 mgKOH/g and an acid value (AV) between These results show that the PUR obtained using used 13-106 mgKOH/g. FTIR and 1H NMR analysis showed the 8 presence of OH groups, confirming the conversion of the fatty acids double bonds (C=H). The glue tests results showed that the polyols with higher viscosity (higher refractive index), results in polyurethane adhesives (PUR) with positive tests. The process scale-up is economically viable. However, more investigation is needed to achieve the required PUR perfor- mance.

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